In my laboratory, we have emphasized the importance of fusing the various levels of inquiry (ultrastructural, experimental, molecular, and genetic) in order to obtain a fuller understanding of developmental processes. The Drosophila oocyte and embryo are uniquely suitable for the fusing of these approaches. Mutations affecting vitellogenesis and early development are easily obtained, and sufficient quantities of material can be generated for molecular approaches. Our current plans are to concentrate on the structuring of the egg cortex and its modification during early development. Structural evidence suggests that the cortex is considerably changed at activation, possibly due to the removal of vitellogenin receptors. Consequently, we will continue our extensive analysis of vitellogenin synthesis and uptake. During early development, cells first form and then move to take on different cellular arrangements. The changes in cell surface will be analyzed by EM and immunological approaches. A number of maternal-effect mutations appear to affect these cellular movements, and these will be analyzed. A detailed molecular and immunological analysis of the early embryonic cell surfaces will be undertaken in order to provide the basis for interpreting mutant embryos. By means of experimental embroyology, our knowledge of the state of determination of cells will be determined and applied to mutants affecting gastrulation. Thus, I believe that a coordinated, structural, molecular, and genetic analysis of the Drosophila embryo is possible.